Capacitors testing

The solution for this problem is the use of an equalisation circuit, which is essential in systems composed by at least six capacitors in series. This equipment monitors each capacitor testing the voltage across each pair of its terminals, and eventually moves charge from one capacitor to another to guarantee the same value of voltage across the series. 

Comparison of impedance-frequency characteristics for various types of capacitors tested by the Matsushita Electrical Industrial Co. of Japan group. 

After densiftcation, external electrode termination and leads are attached for MLC capacitor components, and pin module assembly and IC chip joining is carried out for MLC packages. The devices are then tested to ensure performance and overall reflabiUty. 

Electronic and Electrical Applications. Sulfolane has been tested quite extensively as the solvent in batteries (qv), particularly for lithium batteries. This is because of its high dielectric constant, low volatUity, exceUent solubilizing characteristics, and aprotic nature. These batteries usuaUy consist of anode, cathode polymeric material, aprotic solvent (sulfolane), and ionizable salt (145—156). Sulfolane has also been patented for use in a wide variety of other electronic and electrical appHcations, eg, as a coil-insulating component, solvent in electronic display devices, as capacitor impregnants, and as a solvent in electroplating baths (157—161). 

The basic principle of these methods is to charge a capacitor up to the specified lest voltage and then discharge it through the coil under test. 

Additional tests on a capacitor VT The tests discussed above refer generally to the electromagnetic unit only. To test the whole VT, the following tests are recommended. For the test procedure and results refer to lEC 60186. 

These capacitors differ from standard p.f, improvement capacitors, as they are designed to withstand higher test voltages and have a low internal inductance. They should preferably be non-inflammable, synthetic liquid impregnated and provided with a built-in discharge resistance. For specifications refer to VDE 0675 and VDE 0560 III,... 

Shunt power capacitors of non self-healing types up to and including 1000 V General performance, testing and rating. Safety requirements. Guide for installation and operation 13585-1/1994 BS EN 60931-1/1996... 

Below we discuss briefly recommended tests on a finished capacitor unit based on various lEC recommendations. For standards refer to the list provided at the end of the chapter. 

Routine tests are carried out on each capacitor unit. 

Protection, maintenance and testing of capacitor units 26/839 Table 26.3 Power frequency lest voltages and their duration for voltage tests on a power capacitor unit or bank... 

The above tests refer to dry power frequency voltage withstand tests for indoor units. Outdoor capacitor units will be subjected to a wet test as in lEC 60060-1. 

Every capacitor unit will be subject to an a.c. test at a voltage specified in Table 26.3 at a frequency between 15 and 100 Hz, preferably as close to the rated as possible. During the test no permanent puncture or flashover should occur. 

This is another name for a heat run test. A voltage sufficient to cause an output of the capacitor unit equal to 1.5 times the rated output is applied at the rated frequency and test conducted for at least 48 hours. During the last six hours of the test the temperature rise and tan 5 are measured at least four times. The temperature rise during the last six hours should not exceed 1 C, otherwise the test duration must be extended until the temperature stabilizes to a rise of only l°C. The final test results... 

The lest voltage should be 2.5 V, irrespective of star- or delta-connected units. Tlie capacitor unit should be charged with the test voltage and discharged five times within 10 minutes. Within 5 minutes after the test the unit may be subjected to voltage lest (.3) between the terminals. The... 

One will appreciate that such tests are no guarantee of the minimum life of a capacitor unit. Moreover, it is not expected that such tests can predict the future of the capacitor units. They can, at best, suggest the compliance of the test requirements which should ensure a reasonably prolonged operating life of the capacitors, as envisaged. These tests do provide feedback to the manufacturer on the t uality of the dielectric and the process of insulation adopted and if iiny improvements are required. 

This is an alternative to the ageing test and is applicable for shunt capacitors of 1000 V and above. It is an in-house process test and is carried out on the capacitor elements before they are assembled into a capacitor unit to ascertain their dielectric stability against repeated overvoltages. For the test procedure refer to lEC 60871-2. 

This test is conducted to estimate the working life of a capacitor. Brietly. the test can be conducted in three stages as follows ... 

Shunt power capacitors of the self healing type for a.c. systems having rated voltage up to and including 1000 V Ageing test, self-healing lest and destruction lest 13.341/1992 BS EN 60831-2/1996... 

Shunt capacitors for a.c. power system rated voltage above 1000 V (non-self-healing type) Endurance testing 13925-2/1994 BS 7264-2/1990... 

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